Gas circuit breaker and vacuum circuit breaker are the 2 main types of circuit breaker used in extra high voltage and medium voltage networks. After reviewing the history of these circuit breakers, their present status and technologies are described. As for future technology, computation of interrupting phenomena, SF6 gas less apparatus and expectation of the high voltage vacuum circuit breaker are discussed.

Recently, the technology to examine the transmission capacity accurately from the viewpoint of effective use of the power equipment is requested. Therefore, Tokyo Electric Power Co. and the Japan Research Institute, Ltd. have jointly developed a new conductor temperature estimation program that makes use of the finite element method, as a tool for calculating at high precision the transmission capacity of a cable.This program newly incorporates seasonal changes in air and ground temperature, ground-surface boundary conditions for sunlight and radiation, and temperature changes in the depth direction. Heretofore it has been impossible to vary the load current, but this time it was possible to obtain more realistic simulation results than by the previous stationary-current analysis, by allowing transient-current analysis to which daily and seasonal fluctuations are added.In this report, we proposes the concepts of thermal analysis solver and ground level heat balance model which are basic specifications of program, and, we proposes technique to calculate two or more sections to analyze the movement of heat to lengthening joint of cable. And, we report that the effectiveness of the program was confirmed by the comparison verification of a long-term demonstration test result and the numerical analysis result.

3kV 600A 4H-SiC flat package type pn diodes have been developed and their reverse recovery characteristics have been investigated. In spite of pn junction diodes, the developed diodes have a short reverse recovery time of 0.153μs at room temperature. This diodes have 1/10th lower recovery loss and 1/3rd lower recovery time than those of a commercialized 2.5kV Si diode in spite of high blocking voltage. When this diodes apply to PWM inverter, the carrier frequency that on-state loss is equal to switching loss is 1.45 times the Si diode's frequency at 398K. By using the developed diode, high voltage high frequency inverter operation can be realized.

It has been well known for many years that grounding resistance has a current-dependent characteristic due to soil ionization. Moreover reinforced concrete poles should be treated as a kind of grounding electrode against lightning strokes. However, these characteristics were seldom taken into account for lightning-protection designs. If these characteristics are represented in EMTP models for lightning protection designs, the rationalization of the lightning protection designs for distribution lines is expected.In order to clarify transient behaviors of a system of a grounding electrode and a concrete pole, experiments were conducted with full-scale grounding systems. In this study, the paper described a composite model of a reinforced concrete pole and a grounding electrode for distribution lines and compared the calculated waveforms with measured waveforms of the experiments. The results show that it is necessary to take a current-dependent characteristic into account and treat concrete poles as a kind of grounding electrode.

This paper proposes two types of PSS design method that take into account the robustness for comparably large power systems. The first one is a design method based on H∞ control theory and the second one is a parameter determination method for a standard PSS by using Particle Swarm Optimization (PSO). In order to deal with large-scale systems, a reduced model is developed to get the target system, which preserves major oscillation modes only. The major oscillation modes are selected by using residue concept and the PSS is designed based on the target system. In order to verify the effectiveness, the proposed methods are compared with the other previously proposed method based on Genetic Algorithm (GA) through many numerical simulations.

Lightning surge characteristics of a ground mesh have influence on electromagnetic transient behaviors in low voltage and control circuits. This paper describes experimental and analytical studies on lightning surge characteristics of a ground mesh. The experimental studies are carried out under various conditions. The experimental parameters considering in this measurement include earth resistances, current injection points and injection current waveforms. These measured results are compared with calculated results based on the theoretical studies by Sunde. A comparison of the measured results with the calculated results shows good agreement.

With the urgent need for cost reduction in electric power equipment, investment in equipment will be controlled and the number of aged equipment will increase in the future. Moreover, it is requested that aged equipment should be used to the utmost limit by postponing the replacement to as late a date as possible. At this time, it is important to discuss how we can evaluate and guarantee the residual lifetime of equipment. As a method of replacement postponement, there is an alternative possibility of guaranteeing the lifetime by executing an insulation test on the aged equipment again.The present standards of AC insulation tests for high voltage power equipment in Japan are based on the reliability evaluation according to the Weibull distribution assumed as fault occurrence probability of the equipment. The present evaluation is not considered a proper one as it doesn't take into account non-accidental change of the equipment with time. One of the authors has pointed out this problem in a recent paper.In this paper, we investigated long-time V-t characteristics and the meaning of AC insulation tests for gas-insulated power equipment. Furthermore, we discuss the fault probability when two different levels (waveform or value) of voltage are applied to equipment. Finally, we investigate the feasibility to replacement postponement by executing the insulation test on the aged equipment again.

SF6 gas is widely used in electric power apparatus such as gas insulated switchgears (GIS), because of its superior dielectric properties; however, it has been identified as a greenhouse gas at COP3 in 1997, alternative insulation gases to SF6 are recently investigated. The one of the candidates is CO2 gas, which has lower global warming potential (GWP). However CO2 gas has a lower withstand voltage level than SF6 gas; therefore, it is necessary to rationalize the equipment insulation level and reexamine the insulating test voltage for electric power apparatus as low as possible. From our previous investigation, in SF6 gas insulation system, it is obtained that the insulation requirements of the real surges (called non-standard lightning impulse waveform) are not as severe as those of the standard lightning impulse waveform. This paper describes the evaluation method for real surges, based on insulation characteristics of CO2 gas gaps. Furthermore, the method was applied to typical field overvoltage waveform in the lightning surge time region for 500kV systems and it is obtained that the equivalent peak value of the standard lightning impulse waveform is possibly reduced by 10 to 15 percents.

The higher safety and reliability have been strongly desired under the liberalization of electricity markets and the complexity of power system with dynamic load and distributed generators. The objective of this letter is to express a dynamic load in a polynomial, and to propose a method for voltage stability analysis using a system P-V curve and a load P-V one with dynamic characteristics.

The development of a fault diagnosis system for small wind turbines is necessary; recently, the system of wind-generated power has continued to become outdated, and there have been many cases of damages to the blades of small wind turbines and to the internal areas of the generator due to flying objects and lighting. The early failure diagnostic system of the small wind turbine using impact sensor was proposed, and the failure level was discovered. When the damage at 20 mm exceeded the change of a shock wave, it turned out that the waveform change notably appeared.

A new approach for the continual assessment of winding deformation during short circuit test is proposed. The method is validated through FEM analysis of axially unbalanced axisymmetric configurations. Simulation results are shown to validate the proposed method.